1. Field of the Invention
The present invention generally relates to the field of computer image processing of computer tomography (CT) data and, more particularly, to a system and method for accessing the three-dimensional geometry of large objects using X-ray based methods subject to limitations on radiation doses.
2. Background Description
U.S. Pat. No. 5,416,815, which is incorporated here by reference in its entirety, describes computer tomography (CT) systems and the method of image reconstruction from projections.
The usefulness of getting three dimensional representations of objects under study has long been recognized, in particular, in medicine. Several techniques, more or less invasive, have been developed which allow three dimensional data acquisition. The present invention addresses the case when data acquisition techniques are so invasive that their use has to be minimized. Thus, one has to rely on a limited amount of information gathering to construct a useful three dimensional rendering of the object of study.
Although the principles disclosed here are applicable to quite general settings, medical or otherwise, we will concentrate on the study of the spine of patients afflicted with idiopathic scoliosis. Idiopathic scoliosis is a condition which affects a very large bone structure, the spine. Since X-ray analysis is commonly used in the study of bones (Magnetic Resonance Imaging (MRI) and other non-invasive techniques lack the kind of precision one needs for several purposes like the analysis of scoliosis), the size of the spine and the limited amount of X-ray that a patient can withstand forbid fine X-ray computer tomography (CT) scanning as a method to get a three dimensional representation. Furthermore, the evolutive nature of the condition implies that examinations have to be frequently repeated, with accumulative radiation hazard, which is another reason to look for small doses of radiations in the process of data acquisition.
Idiopathic scoliosis is a little understood disease. It is a progressive three dimensional (3-D) deformation of the spine involving curvature and torsion which affects about 3% of adolescents, one fifth of whom require extensive medical testing to determine whether dramatic and dangerous surgery will be required. A general reference on scoliosis can be found in Moe's Textbook of Scoliosis and Other Spinal Deformities by John E. Lonstein, David S. Bradford, Robert B. Winter and James Ogilvie, 3rd edition, W. B. Saunders & Co., 1995. Many authors have tried to explain the possible etiology of scoliosis. The term "idiopathic", means "different suffering" in Greek: "idiopathic scoliosis" has the sense of "enigmatic scoliosis".
Scoliosis, in general, is a major deformity that involves practically the whole musculo-skeletal system, and probably other systems as well. Attempts to explain the phenomenon have led to some nosological successes in which a minority of patients have been diagnosed as suffering from something other than idiopathic scoliosis. For that disease, however, the mystery remains. How can a major pathological process that changes practically the whole body go unexplained, with an undetected source? This comprises probably one of the most fascinating enigmas of medicine.
Severe scoliosis leads to one of the grandest surgical procedures known to medicine. The primary goal of surgery is to prevent further deterioration, the secondary one is to correct the deformity as much as is still possible. Spinal fusion is the current treatment. It has absolutely nothing to do with the basic etiology and pathophysiology of the disease and does not attempt to treat its cause. It is a crude mechanical approach which can often lead to subsequent problems. Nevertheless, until a better solution is found, it is the best option.